The present invention relates to transducers employed in environments normally harmful to transducer performance and/or components, in general, and to ultrasonic capacitance-type transducers employing a vibratile diaphragm, for use in such environments, in particular.
A transducer is commonly understood to be a device that converts one type of energy such as mechanical vibrations into another form of energy such as an electrical signal or vice versa. Many different types of transducers are employed in a variety of measuring systems for the purpose of measuring such diverse quantities as distance to an object, temperature of a body or pressure of a gas, to cite but a few examples. Polaroid Corporation, for example, of Cambridge, Massachusetts, presently manufactures several different types of self-developing cameras wherein each of said cameras employs an adjustable focus lens systems that is automatically focused by a rangefinder that employs a capacitance-type transducer in the determination of subject distance. Subject distance is established by measuring the elapsed time between the transmission of a burst of ultrasonic energy by the transducer toward a particular subject and the detection by the same transducer of a reflection of said burst of energy from said particular subject. An electrical signal generated by the rangefinder representative of this elapsed time and therefore subject distance, is subsequently employed to precisely control lens system focusing.
A capacitance-type ultrasonic transducer employs a sound generating/detecting vibratile diaphragm consisting of a thin plastic film having a gold layer or coating on one side thereof a few hundred angstroms thick. Under normal circumstances, such as in the case of the automatically focused self-developing cameras mentioned above, the gold vibratile diaphragm coating forms a part of the exterior of the device in which it is utilized and would therefore be in direct physical contact with the atmosphere or environment where the device is located or employed. In most applictions, the environment has little or no harmful effect on either the gold diaphragm coating or on transducer performance. However, in some applications, the atmosphere may contain corrosive gases and foreign particles that may be harmful to transducer components and/or may degrade transducer performance.
Distance or rangefinding devices employing an ultrasonic capacitance-type transducer of the type mentioned above are capable of determining the distance to fairly close objects (within 40 ft.) to within relatively close tolerances (approx..+-.0.5 inch). However, when an attempt was made to employ a rangefinder of this type on the exterior surface of a vehicle where the transducer was exposed to a combination salt-spray and abrasive (sand) environment, the rangefinder either failed to operate or failed to operate properly after a relatively short period of time. Partial or total failure to operate in such an environment was due either to the salt spray entering the rangefinder through openings in or adjacent the transducer and subsequently corroding electrical components therein or to abrasive material striking and thereby abrading the exposed gold coated surface of the vibratile diaphragm, causing a significant deterioration in transducer and therefore rangefinder performance.
The primary object of the present invention is, therefore, to provide a transducer that is capable of being properly operated in an environment normally harmful to transducer performance and/or components.
Another object of the present invention is to provide a capacitance-type ultrasonic transducer that is capable of being properly operated in a corrosive and/or abrasive environment.
A further object of the present invention is to provide a rangefinder incorporating a capacitance-type ultrasonic transducer that is capable of being operated in a corrosive and/or abrasive environment.
Other objects, features and advantages of the present invention will be readily apparent from the following description of the preferred embodiment thereof taken in conjunction with the accompanying drawings.